Googling tells me this “Although cellulose is indigestible by humans, it does form a part of the human diet in the form of plant foods. Small amounts of cellulose found in vegetables and fruits pass through the human digestive system intact. Cellulose is part of the material called “fiber” that dieticians and nutritionists have identified as useful in moving food through the digestive tract quickly and efficiently. Diets high in fiber are thought to lower the risk of colon cancer because fiber reduces the time that waste products stay in contact with the walls of the colon (the terminal part of the digestive tract).” from http://science.jrank.org/pages/1335/Cellulose-Cellulose-digestion.html